Chemical pest control in agriculture and in fruit culture has been used very successfully to control pests during the past seventy years. Every year, more chemicals are developed, apparently with new advantages over their predecessors relating to cost, ease of application, and the varieties of pests controlled. Unfortunately, also for a long time, and currently, it has been discovered that many of these chemicals have undesirable secondary effects on the environment or on other plants and animals, including man. Some of these undesirable effects, due to a cumulative effect on the body or to genetic transmission affecting new generations, have been seen only after many years of continuous use of the chemical; other undesirable effects are seen very fast. For these reasons, there is a tendency to look for solutions with very little or no impact at all on the environment.
One of the first non-chemical solutions was a biological pest control provided by stimulating development of natural predators of pests. A problem with this is that sometimes a predator will eliminate not only a pest but also some of the natural controls, and then a serious ecological problem may result.
Other pest control alternatives to biological and chemical methods involve the modification of some physical variables of the pest habitat; in this way the pest is put in an environment which is unfriendly to its development and reproduction. These kinds of solutions include, among others, refrigeration, humidity reduction, heat application, and oxygen reduction. A problem with this kind of solution is determining the habitat variables to be modified and the magnitude and time of habitat variable modification in order to get desired effects on the pest without harming the species to be protected.
In these kinds of solutions, heat application has been shown to be very useful. One of the first solutions for eliminating microorganisms was the well-known method of pasteurization. This method is only applicable to inanimate substances of animal or plant origin, and cannot be used on live animals or plants. Other methods for pest control using heat have been proposed; such methods are disclosed in U.S. Pat. No. 4,817,329 to Forbes and U.S. Pat. No. 6,279,261 to Binker et al.
Forbes teaches a method to kill insects, such as termites, in an urban structure, such as an insulated space, in which a heated gas, with no phase changes, is insufflated. The gas is at a temperature above the ambient temperature which is lethal for the insect, and the temperature is maintained for a sufficient period of time to kill the insect. In the Forbes method, entrance ducts and exit ducts for the heated gases are installed. Forbes also teaches that the space to be treated has to be insulated with mats in windows and doors in order to facilitate accumulation of heated gases. As a result, the Forbes method cannot be used in open spaces and, therefore, cannot be used in agriculture or fruit production.
Binker et al. also teach a method to kill pests in closed spaces, like mills or food processing plants. The Binker et al. procedure does not require insulating spaces, but this is because the space in which the Binker et al. method is used is normally closed and without windows, like in the urban structures of Forbes. The Binker et al. method is not applicable in open fields like those used in agriculture or fruit production. The most important concerns of Binker et al. are to not contaminate or alter foods in a processing plant, to avoid the introduction of combustion gases, and to control the humidity of the heated air.
Neither Forbes nor Binker et al. teaches a pest control method using heated gases or heated air in an open space in which it is necessary to maintain or preserve, without any harm, living vegetable species like vines, fruit trees, or plants.